The present disclosure relates generally to a motion-controlled arrangement for, and a method of, reading radio frequency (RF) identification (RFID) tags in a venue in real time with an enhanced performance, especially for rapidly and accurately locating and tracking RFID tags associated with items of interest for inventory control.
It is known to deploy a radio frequency (RF) identification (RFID) system in a retail, factory, or warehouse environment, or a like controlled area or venue, for product locationing, product tracking, product identification, and inventory control. For example, in order to take an inventory of items associated with RFID tags in a warehouse environment or venue, it is known to position a plurality of RFID tag readers at overhead, fixed locations, on the ceiling, or at doorways, loading docks, and assembly lines, in the venue, and then, to operate each such reader, under the control of a network host computer or server, to form and steer an interrogation beam, both in azimuth, e.g., over an angle of 360 degrees around a vertical axis, and in elevation, e.g., over an angle of about 90 degrees away from the vertical axis, over a coverage range across any such tags to read their payloads. Each RFID tag is usually attached to, or associated with, an individual item, or to a package for the item, or to a pallet or container for multiple items, or to a freight mover, such as a forklift or truck, for moving such items, packages, or pallets in the venue. Each RFID tag typically includes a tag antenna, a power management section, a radio section, and frequently a logic section, a memory, or both. A multitude of such tags may be in the coverage range of each RFID reader.
In brief, each RFID reader transmits an RF interrogating signal, and each RFID tag, which senses the interrogating RF signal, responds by transmitting a return RF signal. Each RFID tag either generates the return RF signal originally, or reflects back a portion of the interrogating RF signal in a process known as backscatter. The return RF signal may further encode data stored internally in the tag. The return signal is demodulated and decoded into identification data (also known as the payload) by each reader, which thereby identifies, counts, or otherwise interacts with the associated item. The decoded data can denote a serial number, a price, a date, a destination, a location, other attribute(s), or any combination of attributes, and so on. A specific location of any particular RFID-tagged item in the venue is typically determined by having the server process the payloads and capture data from a plurality of such RFID readers by using triangulation/trilateration techniques known in the art.
As advantageous as such known RFID systems have been in identifying, locating and tracking items with RFID tags, especially low-cost passive tags, it has proven difficult in practice to accurately and rapidly locate each tag, especially when one or more of the tags have moved, as well as when there is a multitude, e.g., a tag population of many thousands, of such tags in the venue. In addition, the venue itself has structures, such as shelving and like fixtures, as well as walls, the floor and the ceiling, and even people and moving equipment, all of which and more can reflect and/or scatter and/or absorb the RF signals, thereby causing the RF signals to travel along multiple, disrupted, folded paths and negatively impacting the travel of the RF signals between the RFID tags and the RFID reader. Each RFID reader reads at a certain read rate, for example, about 100-200 tags per second, and it takes a certain, non-negligible amount of time to read an entire tag population. Sometimes, each RFID reader has to read an individual tag more than once to accurately determine its location. When an RFID-tagged item has moved, i.e., when its location has changed to a new location, the time that it takes to provide an update of its new location is negatively affected by the presence of a large number of other tags. It is not always possible to know, at least not immediately, when a particular tag has moved, because the system must typically identify and locate all the tags before it can determine whether any particular tag has moved. The amount of time it takes to determine the new location of a tag that has moved is a linear function of the number of the tags within the coverage range of the reader(s). Real time reading performance, on the order of one second or less, for rapidly determining the new location of a tag that has moved, or for accurately locating any particular tag, is a challenge that known RFID systems have not always adequately met.
To improve the locating of the RFID tags, it is known to utilize a phased antenna array in the RFID system. However, this requires the addition of expensive hardware. It is further known to deploy a video or surveillance system in the venue by positioning a plurality of video cameras throughout the venue. Each video camera is operated to capture and record video streams of images of targets, such as the RFID tags, and to process these video streams to provide additional control, information, and feedback to the RFID system to improve its performance in locating the RFID tags. However, this not only requires the addition of expensive hardware, but also requires additional video processing server resources to process the video streams, and also utilizes excessive server bandwidth.
Accordingly, there is a need to more accurately and rapidly locate such tags, especially in a large RFID tag population, to conserve server bandwidth and video processing server resources, and to enhance the reading performance of such RFID systems.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The arrangement and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.